Composite cathode active material, cathode and lithium battery including the same, and method of preparing the composite cathode active material

ABSTRACT

A composite cathode active material and a cathode and a lithium battery including the composite cathode active material. The composite cathode active material has a core including a plurality of primary particles including a nickel-containing first lithium transition metal oxide having a layered crystal structure; a grain boundary disposed between adjacent primary particles of the plurality of primary particles; and a shell on the core, the shell including a second lithium transition metal oxide having a spinel crystal structure, wherein the grain boundary includes a first composition having a spinel crystal structure.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Pat. Application Serial No.15/860,901, filed on Jan. 3, 2018, and claims priority to and thebenefit of Korean Patent Application No. 10-2017-0083607, filed on Jun.30, 2017, in the Korean Intellectual Property Office, and all thebenefits accruing therefrom under 35 U.S.C. §119, the contents of whichare incorporated herein by reference in their entirety.

BACKGROUND 1. Field

The present disclosure relates to a composite cathode active material, acathode, and a lithium battery including the composite cathode activematerial, and a method of preparing the composite cathode activematerial.

2. Description of the Related Art

In order to achieve miniaturization and high performance of variousdevices, in addition to miniaturization and weight reduction of alithium battery, high energy density is becoming important. That is, ahigh capacity of a lithium battery is becoming important.

A cathode active material having a high capacity has been examined tomanufacture a lithium battery having the characteristics describedabove.

A nickel-based cathode active material may lead to poor lifespancharacteristics and poor thermal stability due to a high amount ofresidual surface lithium and a side reaction caused by cation mixing.

Therefore, there is a need for a method that can prevent deteriorationof battery performance while including a nickel-based cathode activematerial.

SUMMARY

Provided is a composite cathode active material capable of preventingdeterioration of battery performance by suppressing a side reaction on asurface of and inside the composite cathode active material.

Provided is a cathode including the composite cathode active material.

Provided is a lithium battery including the cathode.

Provided is a method of preparing the composite cathode active material.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of an embodiment, a composite cathode activematerial includes: a core including a plurality of primary particlesincluding a nickel-containing first lithium transition metal oxidehaving a layered crystal structure; and a grain boundary disposedbetween adjacent primary particles among the plurality of primaryparticles; and a shell on the core, the shell including a second lithiumtransition metal oxide having a spinel crystal structure, wherein thegrain boundary includes a first composition having a spinel crystalstructure.

According to an aspect of an embodiment, a cathode includes thecomposite cathode active material.

According to an aspect of an embodiment, a lithium battery includes thecathode.

According to an aspect of an embodiment, a method of preparing acomposite cathode active material includes: providing a solutionincluding a precursor of a second lithium transition metal oxide havinga spinel crystal structure; mixing the solution and a nickel-containingfirst lithium transition metal oxide having a layered crystal structureto prepare a mixture; drying the mixture to prepare a dried product; andheat-treating the dried product to prepare the composite cathode activematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1A is a schematic view that partially illustrates an internalstructure of an embodiment of a composite cathode active material;

FIG. 1B is a schematic cross-sectional view of an embodiment of acomposite cathode active material;

FIG. 2 is a graph of intensity (arbitrary units, a.u.) versusdiffraction angle (degrees 2-theta) showing the results of X-raydiffraction (“XRD”) analysis of composite cathode active materialsprepared in Examples 1 to 3 and Comparative Examples 1 and 2;

FIG. 3 is a graph of intensity (a.u.) versus Raman shift (cm⁻¹) showingthe results of Raman analysis of composite cathode active materialsprepared in Examples 1 to 4 and Comparative Example 1;

FIGS. 4A to 4C are images of a cross-section of the composite cathodeactive material prepared in Comparative Example 1, obtained viahigh-angle annular dark field image (“HAADF”) scanning transmissionelectron microscopy (“STEM”) and energy dispersive X-ray spectroscopy(“EDS”);

FIGS. 5A to 5E are HAADF STEM and EDS images of a surface of thecomposite cathode active material prepared in Comparative Example 2;

FIGS. 6A to 6F are HAADF STEM and EDS images of a surface of thecomposite cathode active material prepared in Example 3;

FIGS. 7A and 7B are scanning electron microscope images of thecross-section of the composite cathode active material prepared inComparative Example 1 before and after 50 charge/discharge cycles;

FIGS. 8A and 8B are scanning electron microscope images of thecross-section of the composite cathode active material prepared inExample 3 before and after 50 charge/discharge cycles; and

FIG. 9 is a schematic view of an embodiment of a lithium battery.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list.

As the present inventive concept allows for various changes and numerousembodiments, particular embodiments will be illustrated in the drawingsand described in detail in the written description. However, this is notintended to limit the present inventive concept to particular modes ofpractice, and it is to be appreciated that all changes, equivalents, andsubstitutes that do not depart from the spirit and technical scope areencompassed in the present inventive concept. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the inventiveconcept. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that the terms suchas “including,” “having,” and “comprising” are intended to indicate theexistence of the features, numbers, steps, actions, components, parts,or combinations thereof disclosed in the specification, and are notintended to preclude the possibility that one or more other features,numbers, steps, actions, components, parts, or combinations thereof mayexist or may be added.

Thicknesses of several layers and regions in the drawings may beexaggerated for convenience of explanation. Throughout thespecification, like reference numerals in the drawings denote likeelements. Throughout the specification, it will be understood that whena component, such as a layer, a film, a region, or a plate, is referredto as being “on” another component, the component can be directly on theother component or intervening components may be present thereon.Throughout the specification, while such terms as “first,” “second,”etc., may be used to describe various components, such components mustnot be limited to the above terms. The above terms are used only todistinguish one component from another.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ± 30%, 20%, 10% or 5% of the statedvalue.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

A C rate means a current which will discharge a battery in one hour,e.g., a C rate for a battery having a discharge capacity of 1.6ampere-hours would be 1.6 amperes.

Hereinafter, a composite cathode active material, a method of preparingthe same, and a cathode and a lithium battery including the compositecathode active material, according to example embodiments, will bedescribed in detail.

According to an embodiment, a composite cathode active material includesa core including a plurality of primary particles including anickel-containing first lithium transition metal oxide having a layeredcrystal structure; and a grain boundary disposed between the pluralityof primary particles adjacent to each other; and a shell that isdisposed on the core, wherein the shell includes a second lithiumtransition metal oxide having a spinel crystal structure, and whereinthe grain boundary includes a first composition having a spinel crystalstructure.

Referring to FIGS. 1A and 1B, a composite cathode active material 300includes a core 100 including a plurality of primary particles 10 and agrain boundary 20 disposed between adjacent primary particles of theplurality of primary particles 10; and a shell 200 that is disposed onthe core 100. For example, the plurality of primary particles 10 may becrystallites that have the same crystal structure within the primaryparticles 10. Each of the plurality of primary particles 10 includes anickel-containing first lithium transition metal oxide having a layeredcrystal structure, and the shell 200 includes a second lithiumtransition metal oxide having a spinel crystal structure. For example,the shell 200 may be a coating layer that is disposed on a part of orthe whole surface of the core 100. The grain boundary 20 between theadjacent primary particles of the plurality of primary particles 10includes a first composition having a spinel crystal structure. Thecomposite cathode active material 300 may be a secondary particle formedby agglomeration of the plurality of primary particles 10.

While not wanting to be bound by theory, it is understood that when thecore 100 of the composite cathode active material 300 includes the grainboundary 20 including the first composition having a spinel crystalstructure between the adjacent primary particles of the plurality ofprimary particles 10, lithium ion conduction within the core 100 may befacilitated, and elution of nickel ions from the primary particle 10 inthe core 100 to an electrolyte solution penetrated into the core 100 maybe suppressed. Also, a side reaction of the primary particle 10 and theelectrolyte solution within the core 100 may be suppressed, and thus,cycle characteristics of a lithium battery including the compositecathode active material 300 may improve. Also, an amount of lithiumresidue on surfaces of the plurality of primary particles 10 maydecrease, and thus deterioration of the composite cathode activematerial 300 may be suppressed. Further, gas occurrence may decrease,which may result improvement of thermal stability of the lithiumbattery. Since the first composition having a spinel crystal structureincluded in the grain boundary 20 between adjacent primary particles 10may withstand a volume change of the primary particles 10 during acharge/discharge process, cracks between the primary particles 10 may besuppressed. In this regard, mechanical strength deterioration of thecomposite cathode active material 300 may be suppressed even afterrepeating a charge/discharge process, and thus degradation of thelithium battery may be prevented.

When the shell 200 having a spinel crystal structure is further added ona surface of the core 100, a side reaction of the core 100 and anelectrolyte solution may be effectively prevented. Also, unlike the core100 having a layered crystal structure, since the shell 200 having aspinel crystal structure provides 3-dimensional lithium ion transportpathways, an inner resistance of a lithium battery including thecomposite cathode active material 300 decreases, and thus cyclecharacteristics of the lithium battery may further improve. Also, due tothe shell 200, an amount of lithium residue on a surface of thecomposite cathode active material 300 further decreases, and thusdegradation of the lithium battery may be suppressed, which may resultin a decrease of gas occurrence.

In the composite cathode active material 300, an amount of nickel amongtransition metals included in the first lithium transition metal oxidemay be about 70 mole percent (mol%) or more, about 71 mol% or more,about 75 mol% or more, about 80 mol% or more, about 85 mol% or more,about 90 mol% or more, about 93 mol% or more, about 95 mol% or more, orabout 97 mol% or more, e.g., about 71 mol% to about 99 mol%, about 75mol% to about 98 mol%, or about 80 mol% to about 95 mol%, based on atotal content of transition metals included in the first lithiumtransition metal oxide. When an amount of nickel in the first lithiumtransition metal oxide is about 70 mol% or more, a capacity mayincrease. Therefore, a lithium battery having a high capacity may bemanufactured.

A concentration of at least one transition metal other than nickel inthe grain boundary of the composite cathode active material may begreater than a concentration of at least one transition metal other thannickel in the primary particle. For example, a transition metal in thegrain boundary at a concentration greater than that in the primaryparticle may comprise Mn, Co, Fe, or a combination thereof. Inparticular, a transition metal in the grain boundary at a concentrationgreater than that in the primary particle may be Mn and/or Co.

In the core of the composite cathode active material, the grain boundarydisposed between the adjacent primary particles of 50% or more of theprimary particles among the total primary particles may include thefirst composition. The primary particles that contact the grain boundaryincluding the first composition may be, for example, about 50% or more,about 55% or more, about 60% or more, about 65% or more, about 70% ormore, about 75% or more, about 80% or more, about 85% or more, about 90%or more, about 95% or more, about 96% or more, about 97% or more, about98% or more, or about 99% or more of the total primary particles, e.g.,about 50% to about 99%, about 55% to about 98%, or about 60% to about95% of the total primary particles. That is, the grain boundary betweenthe adjacent primary particles of most of the primary particles includedin the core may include the first composition having a spinel crystalstructure.

In the core of the composite cathode active material, the firstcomposition may be disposed at a homogeneous concentration throughout aninside of the core. In some embodiments, the first composition may havea concentration gradient that changes from a center part to a surfacepart of the core. For example, a concentration of the first compositionmay be low at a center part of the core, and a concentration of thefirst composition may be high at a surface part of the core. Forexample, a concentration of the first composition may be high at acenter part of the core, and a concentration of the first compositionmay be low at a surface part of the core. The first composition may bearranged in the core in the discontinuous manner.

Referring to FIG. 1B, in the core 100 of the composite cathode activematerial 300, the grain boundary 20 may substantially be in the form ofa straight line or rectilinear in cross-section. When the primaryparticles 10 adjacent to the grain boundary 20 have a layered crystalstructure, the primary particles 10 may have a polyhedral shape, andthus the grain boundary 20 adjacent to the primary particles 10 may havea straight line or may be rectilinear in cross-section.

Referring to FIG. 1B, in the composite cathode active material 300, thegrain boundary 20 may be arranged in a direction 21 parallel to asurface of the adjacent primary particle 10, and the direction 21 inwhich the grain boundary 20 is arranged may be different from adirection of a tangent 101 of a nearest outer surface of the core 100.

Referring to FIG. 1B, in the composite cathode active material 300, thecore 100 may include a first grain boundary 32 and a second grainboundary 33, wherein the first grain boundary 32 and the second grainboundary 33 may be disposed directly on the same primary particle 30among the plurality of primary particles 10, and the first grainboundary 32 and the second grain boundary 33 may cross each other at anangle (α) that is determined by a shape of the primary particle 30. Theangle (α) at which the first grain boundary 32 and the second grainboundary 33 cross each other may be in a range of greater than about 0degree to less than about 180 degrees, or, for example, about 10 degreesto about 170 degrees, about 20 degrees to about 160 degrees, about 30degrees to about 150 degrees, about 40 degrees to about 140 degrees,about 50 degrees to about 130 degrees, about 60 degrees to about 120degrees, about 70 degrees to about 110 degrees, or about 80 degrees toabout 110 degrees.

Referring to FIG. 1B, in the composite cathode active material 300, thecore 100 may include a plurality of grain boundaries 32 and 42 that areadjacent to the plurality of primary particles 30 and 40, eachrespectively, wherein the plurality of grain boundaries 32 and 42 arearranged in directions 31 and 41 that are parallel to surfaces of theprimary particles 30 and 40 adjacent to the plurality of grainboundaries 32 and 42, each respectively, and the directions 31 and 41,in which the plurality of grain boundaries 32 and 42 are arranged, eachrespectively, may be different from each other.

Referring to FIG. 1B, in the composite cathode active material 300, thegrain boundaries 20, 32, and 42 may have an average grain boundarylength in a range of about 50 nanometers (nm) to about 1000 nm and anaverage grain boundary thickness in a range of about 1 nm to about 200nm. Directions of the lengths of the grain boundaries 21, 31, and 41 maybe parallel to surfaces of the adjacent primary particles 10, 30, and40, and directions of the thicknesses of the grain boundaries 21, 31,and 41 may be perpendicular to surfaces of the adjacent primaryparticles 10, 30, and 40. For example, the average grain boundary lengthmay be in a range of about 50 nm to about 950 nm, about 100 nm to about900 nm, about 150 nm to about 800 nm, or about 200 nm to about 700 nm.For example, the average grain boundary thickness may be in a range ofabout 2 nm to about 100 nm, about 5 nm to about 100 nm, about 10 nm toabout 100 nm, or about 20 nm to about 100 nm. When the average grainboundary length and the average grain boundary thickness are withinthese ranges, a lithium battery may have improved charge/dischargecharacteristics.

In the composite cathode active material 300, an average particlediameter of the primary particles 10 may be in a range of about 50 nm toabout 500 nm, about 50 nm to about 450 nm, about 50 nm to about 400 nm,about 50 nm to about 350 nm, about 50 nm to about 300 nm, about 50 nm toabout 250 nm, or about 50 nm to about 200 nm, but embodiments are notlimited thereto, and the average particle diameter of the primaryparticles 10 may vary further, as long as it provides improvedcharge/discharge characteristics to a lithium battery.

In the composite cathode active material 300, an average particlediameter of the core 100, which is formed of the agglomerated primaryparticles, may be in a range of about 1 micrometers (µm) to about 30 µm,about 2 µm to about 28 µm, about 4 µm to about 26 µm, about 6 µm toabout 24 µm, about 8 µm to about 22 µm, about 10 µm to about 20 µm,about 12 µm to about 18 µm, about 12 µm to about 16 µm, or about 13 µmto about 15 µm, but embodiments are not limited thereto, and the averageparticle diameter of the core 100 may vary further, as long as it mayprovide suitable charge/discharge characteristics to a lithium battery.

In the composite cathode active material 300, the first composition mayinclude about 0.1 mole (mol) to about 1.3 mol of lithium, based on 1 molof the first composition, about 1.7 mol to about 2.3 mol of a transitionmetal, based on 1 mol of the first composition, and about 3.7 mol toabout 4.3 mol of oxygen, based on 1 mol of the first composition. Forexample, the first composition may include about 0.9 mol to about 1.2mol of lithium, based on 1 mol of the first composition, about 1.8 molto about 2.2 mol of a transition metal, based on 1 mol of the firstcomposition, and about 3.8 mol to about 4.2 mol of oxygen, based on 1mol of the first composition. For example, the first composition mayinclude about 1.0 mol to about 1.1 mol of lithium, based on 1 mol of thefirst composition, about 1.9 mol to about 2.1 mol of a transition metal,based on 1 mol of the first composition, and about 3.9 mol to about 4.1mol of oxygen, based on 1 mol of the first composition.

In the composite cathode active material 300, the first composition mayhave the same composition with that of the second lithium transitionmetal oxide. For example, the first composition may include at least onetransition metal at the same concentration the second lithium transitionmetal oxide includes the at least one transition metal. For example, thefirst composition may be prepared by using the same precursor that isused to prepare the second lithium transition metal oxide.

In the composite cathode active material 300, the spinel crystalstructure of the first composition may have cubic symmetry, e.g., belongto an Fd3m space group. In the composite cathode active material, thespinel crystal structure of the second lithium transition metal oxidemay belong to an Fd3m space group. When the spinel crystal structure ofthe first composition and/or the second lithium transition metal oxidebelongs to an Fd3m space group, cycle characteristics and thermalstability of a lithium battery including the composite cathode activematerial may improve.

In the composite cathode active material 300, the grain boundary 20 mayfurther include a lithium transition metal oxide, a lithium-freetransition metal oxide, or a mixture thereof, which is a secondcomposition. The second composition may include an amorphous structure,a layered crystal structure, a spinel crystal structure, a polyvalentanion crystal structure, or a combination thereof. That is, the grainboundary 20 may further include the second composition having acomposition different from that of the first composition or anothercrystal structure within the scope that does not deterioratecharge/discharge characteristics of a lithium battery.

In the composite cathode active material 300, the first lithiumtransition metal oxide may include about 0.1 mol to about 1.3 mol oflithium, based on 1 mol of the first lithium transition metal oxide,about 0.7 mol to about 0.99 mol of nickel, based on 1 mol of the firstlithium transition metal oxide, about 0.01 mol to about 0.3 mol of atransition metal other than nickel, based on 1 mol of the first lithiumtransition metal oxide, and about 1.7 mol to about 2.3 mol of oxygen,based on 1 mol of the first lithium transition metal oxide.

For example, the first lithium transition metal oxide may be representedby Formula 1:

In Formula 1, M includes nickel and at least one non-nickel Group 4 toGroup 13 element; an amount of nickel in M is in a range of about 70mol% to less than about 100 mol%, based on a total content of M; and0.9<_a<_1.1.

For example, the first lithium transition metal oxide may be representedby Formula 2:

In Formula 2, M1, M2, and M3 are different and each independentlyincludes manganese (Mn), vanadium (V), chromium (Cr), iron (Fe), cobalt(Co), zirconium (Zr), rhenium (Re), aluminum (Al), boron (B), germanium(Ge), ruthenium (Ru), tin (Sn), titanium (Ti), niobium (Nb), molybdenum(Mo), or platinum (Pt); and 0.9≤a≤1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.3,0≤e<0.1, and b+c+d+e=1.

For example, in an embodiment of Formula 2 in which M1 and M2 of Formula2 are Co and Mn, respectively, the first lithium transition metal oxidemay be represented by Formula 3:

In Formula 3, M3′ includes vanadium (V), chromium (Cr), iron (Fe),zirconium (Zr), rhenium (Re), aluminum (Al), boron (B), germanium (Ge),ruthenium (Ru), tin (Sn), titanium (Ti), niobium (Nb), molybdenum (Mo),or platinum (Pt); and 0.9≤a≤1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.3, 0≤e<0.1,and b+c+d+e=1.

In the composite cathode active material, the first lithium transitionmetal oxide may include first layer-structured crystals that belong to aC2/m space group, second layer-structure crystals that belong to an R3mspace group, or a combination thereof. The first lithium transitionmetal oxide may be a composite of the first layer-structured crystalsand the second layer-structure crystals.

For example, the first lithium transition metal oxide may include secondlayer-structure crystals that have a composition represented by Formula4a and belonging to a C2/m space group; and third layer-structurecrystals that have a composition represented by Formula 4b and belongingto an R3m space group:

and

In Formula 4b, M‴ includes nickel and manganese (Mn), vanadium (V),chromium (Cr), iron (Fe), cobalt (Co), zirconium (Zr), rhenium (Re),aluminum (Al), boron (B), germanium (Ge), ruthenium (Ru), tin (Sn),titanium (Ti), niobium (Nb), molybdenum (Mo), platinum (Pt), or acombination thereof. At least a part of M is Ni. An amount of Ni in Mmay be about 70 mol% or more, based on a total content of M.

For example, the first lithium transition metal oxide may be representedby Formula 4c:

In Formula 4c, M″ includes nickel (Ni) and cobalt (Co), manganese (Mn),vanadium (V), chromium (Cr), iron (Fe), zirconium (Zr), rhenium (Re),aluminum (Al), boron (B), germanium (Ge), ruthenium (Ru), tin (Sn),titanium (Ti), niobium (Nb), molybdenum (Mo), platinum (Pt), or acombination thereof. At least a part of M is Ni. An amount of Ni in Mmay be about 70 mol% or more, based on a total content of M; and 0<a<1.

In the composite cathode active material, the second lithium transitionmetal oxide may be represented by Formula 5:

In Formula 5, M includes manganese and selected non-manganese Group 4 toGroup 13 element; and 1.0≤b≤1.1.

For example, the second lithium transition metal oxide may berepresented by Formula 6:

In Formula 6, M4 and M5 are different and each independently includescobalt (Co), nickel (Ni), vanadium (V), chromium (Cr), iron (Fe),zirconium (Zr), rhenium (Re), aluminum (Al), boron (B), germanium (Ge),ruthenium (Ru), tin (Sn), titanium (Ti), niobium (Nb), molybdenum (Mo),or platinum (Pt); and 0.9≤a≤1.1,0<b≤2.0, 0≤c<2.0, 0≤d<0.1, and b+c+d=2.

For example, the second lithium transition metal oxide may berepresented by Formula 7:

In Formula 7, M5′ includes vanadium (V), chromium (Cr), iron (Fe),zirconium (Zr), rhenium (Re), aluminum (Al), boron (B), germanium (Ge),ruthenium (Ru), tin (Sn), titanium (Ti), niobium (Nb), molybdenum (Mo),or platinum (Pt); and 0.9≤a≤1.1,0<b<2.0, 0<c<2.0, 0≤d<0.1, and b+c+d=2.

In the composite cathode active material 300, a thickness of the shell200 may be about 300 nm or less, about 250 nm or less, about 200 nm orless, about 150 nm or less, about 100 nm or less, about 90 nm or less,about 80 nm or less, about 70 nm or less, about 60 nm or less, about 50nm or less, about 40 nm or less, about 30 nm or less, about 20 nm orless, or about 10 nm or less. When the thickness of the shell is withinthese ranges, cycle characteristics and thermal stability of a lithiumbattery including the composite cathode active material may improve.

In the composite cathode active material 300, the sum of amounts of thesecond lithium transition metal oxide and the first composition may beabout 10 weight percent (wt%) or less, about 9 wt% or less, about 8 wt%or less, about 7 wt% or less, about 6 wt% or less, about 5 wt% or less,about 4 wt% or less, about 3.5 wt% or less, about 3 wt% or less, about2.5 wt% or less, about 2 wt% or less, or about 1 wt% or less, based onthe total weight of the composite cathode active material, e.g., about10 wt% to about 0.001 wt%, about 9 wt% to about 0.01 wt%, or about 8 wt%to about 0.1 wt%, or about 7 wt% to about 0.5 wt%, based on the totalweight of the composite cathode active material. The sum of amounts ofthe second lithium transition metal oxide and the first composition maybe about 0.01 wt% or more, about 0.05 wt% or more, about 0.1 wt% ormore, about 0.2 wt% or more, about 0.3 wt% or more, about 0.4 wt% ormore, or about 0.5 wt% or more. When the sum of amounts of the secondlithium transition metal oxide and the first composition is within theseranges, cycle characteristics and thermal stability of a lithium batteryincluding the composite cathode active material may improve.

A crack growth of a cross-section of the composite cathode activematerial after 50 cycles of charging and discharging of a lithiumbattery including the composite cathode active material is defined byEquation 1, and the crack growth may be about 6% or less, about 5% orless, about 4% or less, about 3% or less, or about 2% or less, e.g.,about 6% to about 0.01 %, about 5% to about 0.1 %, about 4% to about0.5%, or about 3% to about 1%. When the composite cathode activematerial has a low crack growth of about 6% or less, deterioration ofthe composite cathode active material may be prevented even afterrepeating the charging and discharging for a long period of time.

$\begin{array}{l}{\text{Crack growth}(\%) = \lbrack ( \text{pore area of cross-section of composite} ) )} \\\text{cathode active material particles after 50 charge/discharge} \\\text{cycles - pore area of cross-section of composite cathode active} \\{( \text{material particles before charge/discharge cycles} )\text{/pore area of}} \\\text{cross-section of composite cathode active material particles before} \\{( \text{charge/discharge cycles} \rbrack \times 100\%}\end{array}$

In Equation 1, the term “pore area” denotes an area of pores, forexample, shown in black in the composite cathode active material in FIG.8A.

According to an embodiment, a cathode may include the composite cathodeactive material.

A cathode is prepared as follows. For example, the composite cathodeactive material, a conducting agent, a binder, and a solvent are mixedto prepare a cathode active material composition. In some embodiments,the cathode active material composition may be directly coated and driedon an aluminum current collector to prepare a cathode plate. In someembodiments, the cathode active material composition may be cast on aseparate support to form a cathode active material film, which may thenbe separated from the support and laminated on an aluminum currentcollector to prepare a cathode plate having a cathode active materiallayer formed thereon.

The conducting agent may be carbon black, graphite particulates, naturalgraphite, artificial graphite, acetylene black, and Ketjen black; carbonfibers; carbon nanotubes; metal powder or metal fibers or metal tubes ofcopper, nickel, aluminum, or silver; or a conducting polymer such as apolyphenylene derivative, but embodiments are not limited thereto. Anysuitable material available as a conducting agent in the art may beused.

Examples of the binder are a vinylidene fluoride/hexafluoropropylenecopolymer, polyvinylidene fluoride (“PVDF”), polyacrylonitrile,polymethyl methacrylate, polytetrafluoroethylene (“PTFE”), mixturesthereof, and a styrene butadiene rubber polymer, but embodiments are notlimited thereto. Any suitable material available as a binding agent inthe art may be used. Examples of the solvent are N-methyl-pyrrolidone(“NMP”), acetone, or water, but embodiments are not limited thereto. Anysuitable material available as a solvent in the art may be used.

In some embodiments, pores may be formed in the cathode by furtherincluding a plasticizing agent in the cathode active materialcomposition.

Amounts of the composite cathode active material, the conducting agent,the binder, and the solvent may be in ranges that are used in lithiumbatteries. At least one of the conducting agent, the binder, and thesolvent may be omitted according to the use and the structure of thelithium battery.

In some embodiments, the cathode may further include a second cathodeactive material in addition to the composite cathode active material.

The second cathode active material is a lithium-containing metal oxide,which may be any suitable material available in the art. For example,the second cathode active material may a lithium composite oxideincluding cobalt, manganese, nickel, or a combination thereof. Examplesof the second cathode active material may be Li_(a)A₁₋ _(b)B’_(b)D′₂(where 0.90 ≤ a ≤ 1.0 and 0 ≤ b ≤ 0.5); Li_(a)E₁-_(b)B’_(b)O_(2-c)D’_(c)(where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05);LiE_(2-b)B’_(b)O_(4-c)D’_(c) (where 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05);Li_(a)Ni_(1-b-) _(c)Co_(b)B’_(c)D’_(a) (where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li_(a)Ni_(1-b-)_(c)Co_(b)B’_(c)O_(2-a)F′_(α) (where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.5, 0 ≤ c≤ 0.05, and 0 < α < 2); Li_(a)Ni_(1-b-) _(c)C_(Ob)B’_(c)O₂₋,F′₂ (where0.90 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2);Li_(a)Ni_(1-b-) _(c)Mn_(b)B’_(c)D′_(α) (where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li_(a)Ni_(1-b-)_(c)Mn_(b)B’_(c)O_(2-α)F′_(α) (where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.5, 0 ≤ c≤ 0.05, and 0 < α < 2); Li_(a)Ni_(1-b-) _(c)Mn_(b)B’_(c)O_(2-α)F′₂(where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2);Li_(a)Ni_(b)E_(c)G_(d)O₂ (where 0.90 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.9, 0 ≤ c ≤0.5, and 0.001 ≤ d ≤ 0.1.); Li_(a)Ni_(b)Co_(c)Mn_(d)G_(e)O₂ (where 0.90≤ a ≤ 1.0, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤0.5, and 0.001 ≤ e ≤ 0.1.);Li_(a)NiG_(b)O₂ (where 0.90 ≤ a ≤ 1.0 and 0.001 ≤ b ≤ 0.1.);Li_(a)CoG_(b)O₂ (where 0.90 ≤ a ≤ 1.0 and 0.001 ≤ b ≤ 0.1.);Li_(a)MnG_(b)O₂ (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1.);Li_(a)Mn₂G_(b)O₄ (where 0.90 ≤ a ≤ 1.0 and 0.001 ≤ b ≤ 0.1.); QO₂; QS₂;LiQS₂; V₂O₅; LiV₂O₅; Lil’O₂; LiNiVO₄; Li(_(3-f))J₂(PO₄)₃ (where 0 ≤ f ≤2); Li(_(3-f))Fe₂(PO₄)₃ (where 0 ≤ f ≤ 2); and LiFePO₄.

In the formulae above, A may include nickel (Ni), cobalt (Co), manganese(Mn), or a combination thereof; B′ may include aluminum (Al), nickel(Ni), cobalt (Co), manganese (Mn), chromium (Cr), iron (Fe), magnesium(Mg), strontium (Sr), vanadium (V), a rare earth element, or acombination thereof; D′ may include oxygen (O), fluorine (F), sulfur(S), phosphorus (P), or a combination thereof; E may include cobalt(Co), manganese (Mn), or a combination thereof; F′ may include fluorine(F), sulfur (S), phosphorus (P), or a combination thereof; G may includealuminum (Al), chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg),lanthanum (La), cerium (Ce), strontium (Sr), vanadium (V), or acombination thereof; Q may include titanium (Ti), molybdenum (Mo),manganese (Mn), or a combination thereof; I′ may include chromium (Cr),vanadium (V), iron (Fe), scandium (Sc), yttrium (Y), or a combinationthereof; and J may include vanadium (V), chromium (Cr), manganese (Mn),cobalt (Co), nickel (Ni), copper (Cu), or a combination thereof.

The compounds listed above as cathode active materials may have asurface coating layer (hereinafter, also referred to as “coatinglayer”). Alternatively, a mixture of the compound being those listedabove and a compound without a coating layer may be used. In someembodiments, the coating layer may include an oxide, a hydroxide, anoxyhydroxide, an oxycarbonate, a hydroxycarbonate, or a combinationthereof. In some embodiments, the compounds for the coating layer may beamorphous or crystalline. In some embodiments, the coating element forthe coating layer may be magnesium (Mg), aluminum (Al), cobalt (Co),potassium (K), sodium (Na), calcium (Ca), silicon (Si), titanium (Ti),vanadium (V), tin (Sn), germanium (Ge), gallium (Ga), boron (B), arsenic(As), zirconium (Zr), or a mixture thereof. The coating layer may beformed using any suitable method (for example, a spray coating method ora dipping method) that does not adversely affect the physical propertiesof the cathode active material when a compound of the coating element isused. Any suitable coating method may be well understood by one ofordinary skill in the art, and thus a detailed description thereof willbe omitted.

According to an embodiment, a lithium battery includes a cathodeincluding the composite cathode active material. The lithium battery maybe manufactured as follows.

First, a cathode is prepared according to a method of preparing thecathode described above.

Next, an anode is prepared as follows. The anode may be prepared in thesame manner as the cathode, except that an anode active material is usedinstead of the composite cathode active material. Also, the sameconducting agent, binder, and solvent used in the preparation of thecathode may be used in the preparation of an anode active materialcomposition.

For example, an anode active material, a conducting agent a binder, anda solvent are mixed together to prepare an anode active materialcomposition. In some embodiments, the anode active material compositionmay be directly coated on a copper current collector to prepare an anodeplate. In some embodiments, the anode active material composition may becast on a separate support to form an anode active material film, whichmay then be separated from the support and laminated on a coppercollector to prepare an anode plate.

The anode active material may be any suitable material that is generallyused in the art. Examples of the anode active material may includelithium, a metal that is alloyable with lithium, a transition metaloxide, a non-transition metal oxide, and a carbonaceous material.

For example, the metal alloyable with lithium may be Si, Sn, AI, Ge, Pb,Bi, Sb, an Si—Y′ alloy (where, Y′ is an alkali metal, an alkaline earthmetal, a Group 13 element, a Group 14 element, a transition metal, arare earth element, or a combined element thereof, and is not Si); or aSn—Y′ alloy (where, Y′ is an alkali metal, an alkaline earth metal, aGroup 13 element, a Group 14 element, a transition metal, a rare earthelement, or a combined element thereof, and is not Sn). Examples of theelement Y′ may include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb,Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt,Cu, Ag, Au, Zn, Cd, B, AI, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po,or a combination thereof.

Examples of the transition metal oxide may include a lithium titaniumoxide, a vanadium oxide, and a lithium vanadium oxide.

Examples of the non-transition metal oxide may include SnO₂ and SiO_(x)(where 0<×<2).

The carbonaceous material may be crystalline carbon, amorphous carbon,or a mixture thereof. Examples of the crystalline carbon may includenatural graphite and artificial graphite, each of which has an amorphousshape, a plate shape, a flake shape, a spherical shape, or a fibershape. Examples of the amorphous carbon may include soft carbon(low-temperature calcined carbon), hard carbon, meso-phase pitchcarbide, and calcined cokes.

Amounts of the anode active material, the conducting agent, the binder,and the solvent may be may be in ranges that are used in lithiumbatteries.

Then, the cathode and the anode may be separated by a separator, and theseparator may be any of various suitable separators that are typicallyused in a lithium battery. In particular, the separator may include amaterial that has a low resistance to migration of ions of anelectrolyte and an excellent electrolytic solution-retaining ability.For example, the separator may glass fibers, polyester, Teflon,polyethylene, polypropylene, polytetrafluoroethylene (“PTFE”), or acombination thereof, each of which may be non-woven or woven fabric. Forexample, a rollable separator including polyethylene or polypropylenemay be used for a lithium ion battery. A separator with a good organicelectrolytic solution-retaining ability may be used for a lithium ionpolymer battery. For example, the separator may be manufactured in thefollowing manner.

A polymer resin, a filler, and a solvent may be mixed together toprepare a separator composition. Then, the separator composition may bedirectly coated on an electrode, and then dried to form the separator.In some embodiments, the separator composition may be cast on a supportand then dried to form a separator film, which may then be separatedfrom the support and laminated on an electrode to form the separator.

The polymer resin used to manufacture the separator may be any suitablematerial that is used as a binder for an electrode plate. Examples ofthe polymer resin are a vinylidenefluoride/hexafluoropropylenecopolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile,polymethylmethacrylate and a mixture thereof.

Next, an electrolyte is prepared.

In some embodiments, the electrolyte may be an organic electrolytesolution. In some embodiments, the electrolyte may be in a solid phase.Examples of the electrolyte are boron oxide and lithium oxynitride. Anysuitable material available as a solid electrolyte in the art may beused. In some embodiments, the solid electrolyte may be formed on theanode by, for example, sputtering.

In some embodiments, the organic electrolyte solution may be prepared bydissolving a lithium salt in an organic solvent.

The organic solvent may be any suitable solvent available as an organicsolvent in the art. In some embodiments, the organic solvent may bepropylene carbonate, ethylene carbonate, fluoroethylene carbonate,butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethylcarbonate, methylpropyl carbonate, ethylpropyl carbonate,methylisopropyl carbonate, dipropyl carbonate, dibutyl carbonate,benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran,y-butyrolactone, dioxirane, 4-methyldioxirane, N,N-dimethyl formamide,dimethyl acetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane,sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethyleneglycol, dimethyl ether, or a mixture thereof.

In some embodiments, the lithium salt may be any suitable materialavailable as a lithium salt in the art. In some embodiments, the lithiumsalt may be LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiCIO₄, LiCF₃SO₃,Li(CF₃SO₂)₂N, LiC4F₉SO₃, LiAIO₂, LiAICI₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x and y are eachindependently a natural number), LiCI, LiI, or a mixture thereof.

Referring to FIG. 9 , a lithium battery 1 includes a cathode 3, an anode2, and a separator 4. In some embodiments, the cathode 3, the anode 2,and the separator 4 may be wound or folded, and then sealed in a batterycase 5. In some embodiments, the battery case 5 may be filled with anorganic electrolytic solution and sealed with a cap assembly 6, therebycompleting the manufacture of the lithium battery 1. In someembodiments, the battery case 5 may be a cylindrical type, a rectangulartype, or a thin-film type. For example, the lithium battery 1 may be alarge-sized thin-film type battery. In some embodiments, the lithiumbattery 1 may be a lithium ion battery.

In some embodiments, the separator may be disposed between the cathodeand the anode to form a battery assembly. In some embodiments, thebattery assembly may be stacked in a bi-cell structure and impregnatedwith the organic electrolytic solution. In some embodiments, theresultant assembly may be put into a pouch and hermetically sealed,thereby completing the manufacture of a lithium ion polymer battery.

In some embodiments, a plurality of battery assemblies may be stacked toform a battery pack, which may be used in any device that requires highcapacity and high output, for example, in a laptop computer, a smartphone, or an electric vehicle.

The lithium battery may have improved lifetime characteristics and highrate characteristics, and thus may be used in an electric vehicle (EV),for example, in a hybrid vehicle such as a plug-in hybrid electricvehicle (PHEV). The lithium battery may be applicable to the high-powerstorage field. For example, the lithium battery may be used in anelectric bicycle or a power tool.

When the lithium battery is charged to a high voltage of about 4.5 V orgreater with respect to lithium during an initial charging process, thespinel crystal structure belonging to an Fd3m space group in the secondlithium transition metal oxide of the shell, which is a coating layer,may be activated, and thus an additional charging capacity/dischargecapacity may be used. Therefore, an initial charge/discharge capacity ofthe lithium battery may improve.

According to an embodiment, a method of preparing a composite cathodeactive material includes preparing a solution comprising a precursor ofa second lithium transition metal oxide having a spinel crystalstructure; preparing a mixture by mixing the solution and anickel-containing first lithium transition metal oxide having a layeredcrystal structure; preparing a dried product by drying the mixture; andheat-treating the dried product.

A precursor of the second lithium transition metal oxide having a spinelcrystal structure used in the preparing of the solution including theprecursor of the second lithium transition metal oxide may be a nitrate,a sulfate, or a chlorate of a transition metal, but embodiments are notlimited thereto, and any suitable soluble salt including a transitionmetal available in the art may be used. Examples of the soluble salt mayinclude Co(NO₃)₂·H₂O and Mn(NO₃)₂·4H₂O. The solution may include theprecursor of the second lithium transition metal oxide and a solventthat may dissolve the precursor of the second lithium transition metaloxide. A type of the solvent is not particularly limited, and anysuitable solvent available as a solvent in the art may be used. Thesolvent may be distilled water.

In the preparing of the mixture, an amount of the solution may be about50 parts by weight or less, about 45 parts by weight or less, about 40parts by weight or less, about 35 parts by weight or less, about 30parts by weight or less, about 25 parts by weight or less, about 20parts by weight or less, or about 10 parts by weight or less, based on100 parts by weight of the nickel-containing first lithium transitionmetal oxide. In the mixture, as a concentration of the first lithiumtransition metal oxide increases, coating a surface and inside of thecomposite cathode active material may be evenly performed.

In the preparing of the mixture, an amount of a solvent contained in thesolution may be about 50 parts by weight or less, about 45 parts byweight or less, about 40 parts by weight or less, about 35 parts byweight or less, about 30 parts by weight or less, about 25 parts byweight or less, about 20 parts by weight or less, or about 10 parts byweight or less, based on 100 parts by weight of the nickel-containingfirst lithium transition metal oxide. In the mixture, when aconcentration of the nickel-containing first lithium transition metaloxide is too low, a surface and inside of the composite cathode activematerial may not be evenly coated with a composition having a spinelcrystal structure.

In the preparing of the mixture, an amount of the precursor of thesecond lithium transition metal oxide may be about 10 parts by weight orless, about 9 parts by weight or less, about 8 parts by weight or less,about 7 parts by weight or less, about 6 parts by weight or less, about5 parts by weight or less, about 4 parts by weight or less, about 3.5parts by weight or less, about 3 parts by weight or less, about 2.5parts by weight or less, about 2 parts by weight or less, or about 1part by weight or less, based on 100 parts by weight of the firstlithium transition metal oxide.

In the preparing of the dried product, a solvent may be removed. Thepreparing of the dried product may be performed in an oven at atemperature of 120° C. for about 1 hour to about 30 hours, but thetemperature and the period of time are not limited thereto but may bechanged within the scope where a composition having a spinel crystalstructure may be formed on a surface of the core and in the grainboundary of the composite cathode active material.

The heat-treating of the dried product may be performed at a temperaturein a range of about 650° C. to about 800° C., about 650° C. to about750° C., or about 700° C. to about 750° C., and an oxidizing atmosphereincludes an oxidizing gas such as oxygen or air. A period of time forthe heat-treating may be in a range of about 3 hours to about 20 hours,about 3 hours to about 15 hours, about 3 hours to about 10 hours, about3 hours to about 7 hours, or about 4 hours to about 6 hours, but thetemperature ranges, atmosphere, or period of time are not limitedthereto and may be changed within the scope where a composition having aspinel crystal structure may be formed on a surface of the core and inthe grain boundary of the composite cathode active material.

One or more embodiments will now be described in more detail withreference to the following examples. However, these examples are notintended to limit the scope of the one or more embodiments.

EXAMPLES Preparation of Composite Cathode Active Material Example 1:Ni91 + LiMnCoO₄ Spinel 0.5 wt% (Powder:Distilled Water =100:40)

100 parts by weight of Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, asa first lithium transition metal oxide, was prepared.

As a precursor of a second transition metal oxide, 0.5 parts by weightof a precursor mixture including Co(NO₃)₂·H₂O and Mn(NO₃)₂·4H₂O at amolar ratio of 1:1 was prepared. The precursor mixture was added to 40parts by weight of distilled water, and the resultant was stirred at 80°C. for 1 minute to prepare an aqueous solution.

The aqueous solution thus prepared was added to 100 parts by weight ofLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, and the resultant wasstirred at 80° C. for 5 minutes to prepare a mixture.

The mixture was dried in an oven at 120° C. for 12 hours to prepare adried product.

The dried product was placed in a furnace and heat-treated therein undera flow of oxygen at 720° C. for 5 hours to prepare a composite cathodeactive material.

During the heat-treating process, a LiMnCoO₄ coating layer having aspinel crystal structure was formed on a surface of aLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ core and in a grain boundarybetween adjacent primary particles among a plurality of primaryparticles.

Example 2: Ni91 + LiMnCoO₄ Spinel 1.0 wt% (Powder:Distilled Water=100:40)

A composite cathode active material was prepared in the same manner asin Example 1, except that 1 part by weight of a precursor mixtureincluding Co(NO₃)₂·H₂O and Mn(NO₃)₂·4H₂O at a molar ratio of 1:1, as aprecursor of a second transition metal oxide, based on 100 parts byweight of Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, as a firstlithium transition metal oxide, was used.

During the heat-treating process, a LiMnCoO₄ coating layer having aspinel crystal structure was formed on a surface of aLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ core and in a grain boundarybetween adjacent primary particles among a plurality of primaryparticles.

Example 3: Ni91 + LiMnCoO₄ Spinel 2.0 wt% (Powder:Distilled Water=100:40)

A composite cathode active material was prepared in the same manner asin Example 1, except that 2 parts by weight of a precursor mixtureincluding Co(NO₃)₂·H₂O and Mn(NO₃)₂·4H₂O at a molar ratio of 1:1, as aprecursor of a second transition metal oxide, based on 100 parts byweight of Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, as a firstlithium transition metal oxide, was used.

During the heat-treating process, a LiMnCoO₄ coating layer having aspinel crystal structure was formed on a surface of aLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ core and in a grain boundarybetween adjacent primary particles among a plurality of primaryparticles.

Example 4: Ni91 + LiMnCoO₄ Spinel 8.0 wt% (Powder:Distilled Water=100:40)

A composite cathode active material was prepared in the same manner asin Example 1, except that 8 parts by weight of a precursor mixtureincluding Co(NO₃)₂·H₂O and Mn(NO₃)₂·4H₂O at a molar ratio of 1:1, as aprecursor of a second transition metal oxide, based on 100 parts byweight of Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, as a firstlithium transition metal oxide, was used.

During the heat-treating process, a LiMnCoO₄ coating layer having aspinel crystal structure was formed on a surface of aLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ core and in a grain boundarybetween adjacent primary particles.

Comparative Example 1: Ni91 Alone

Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, as a first lithiumtransition metal oxide, was used alone as a composite cathode activematerial.

Comparative Example 2: Ni91 + LiMnCoO₄ Spinel 1 wt% (Powder:DistilledWater =100:100)

100 parts by weight of Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, asa first lithium transition metal oxide, was prepared.

As a precursor of a second transition metal oxide, 1 part by weight of aprecursor mixture including Co(NO₃)₂·H₂O and Mn(NO₃)₂·4H₂O at a molarratio of 1:1 was prepared. The precursor mixture was added to 100 partsby weight of distilled water, and the resultant was stirred at 80° C.for 1 minute to prepare an aqueous solution.

The aqueous solution thus prepared was added to 100 parts by weight ofLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ powder, and the resultant wasstirred at 80° C. for 5 minutes to prepare a mixture.

The mixture was dried in an oven at 120° C. for 12 hours to prepare adried product.

The dried product was placed in a furnace and heat-treated therein undera flow of oxygen at 720° C. for 5 hours to prepare a composite cathodeactive material.

During the heat-treating process, a LiMnCoO₄ coating layer having aspinel crystal structure was formed on a surface of aLi_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ core.

Manufacture of Half Cell Example 5 Preparation of Cathode

The composite cathode active material prepared in Example 1, acarbonaceous conducting agent (Denka Black), and polyvinylidene fluoride(PVdF) at a weight ratio of 92:4:4 were mixed to prepare a mixture. Themixture was mixed with N-methyl-pyrrolidone (NMP) in an agate mortar toprepare a slurry. The slurry was bar-coated on an aluminum currentcollector having a thickness of about 15 µm, dried at room temperature,dried again in vacuum at 120° C., and then roll-pressed and punched toprepare a cathode plate having a thickness of about 55 µm.

Manufacture of Coin Cell

The cathode plate was used as a cathode, lithium was used as a counterelectrode, a PTFE separator was used as a separator, and a solutionprepared by dissolving 1.15 Molar LiPF₆ in a solvent mixture includingethylene carbonate (EC) + ethylmethylcarbonate (EMC) + dimethylcarbonate (DMC) at a volume ratio of 3:4:3 was used as an electrolyte,and thus a coin cell was manufactured.

Examples 6 to 8

Coin cells were each manufactured in the same manner as in Example 5,except that each of the composite cathode active materials prepared inExamples 2 to 4 was used instead of the composite cathode activematerial prepared in Example 1.

Comparative Examples 3 and 4

Coin cell were each manufactured in the same manner as in Example 5,except that each of the composite cathode active materials prepared inComparative Examples 1 and 2 was used instead of the composite cathodeactive material prepared in Example 1.

Evaluation Example 1: XRD Spectrum Evaluation

As shown in FIG. 2 , the XRD spectrum of the composite cathode activematerials prepared in Examples 1 to 3 and Comparative Examples 1 and 2were substantially the same. Thus, it was confirmed that structuralchange of Li_(1.03)Ni_(0.91)Co_(0.06)Mn_(0.03)O₂ due to coating did notoccur or was insignificant.

Evaluation Example 2: Raman Spectrum Evaluation

As shown in FIG. 3 , maximum peaks of the composite cathode activematerials prepared in Examples 1 to 4 in the Raman spectrum shiftedright as those were 530 cm⁻ ¹ or greater.

The shift of the maximum peaks shows that a coating layer having aspinel crystal structure was formed in and on the core of the firstlithium transition metal oxide.

Evaluation Example 3: Surface Composition Evaluation

FIGS. 4A to 4C are high-angle annular dark field image (HAADF) STEM andenergy dispersive X-ray spectroscopy (EDS) images of the compositecathode active material prepared in Comparative Example 1, where thecomposite cathode active material was formed when a plurality of primaryparticles agglomerate each other.

FIGS. 5A to 5E are HAADF STEM and EDS images of the composite cathodeactive material prepared in Comparative Example 2, where the compositecathode active material included a secondary particle core, which wasformed when a plurality of primary particles agglomerate each other, anda spinel coating layer disposed on the core.

FIGS. 6A to 6F are HAADF STEM and EDS images of a surface of thecomposite cathode active material prepared in Example 3, wherein thecomposite cathode active material included a secondary particle core,which was formed when a plurality of primary particles agglomerate eachother, and a coating layer disposed in a grain boundary in the core andon a surface of the core.

As shown in FIGS. 4A to 4C, it was confirmed that Co and Mn were evenlydistributed throughout the whole core.

As shown in FIGS. 5B to 5E, it was confirmed that Ni and O were evenlydistributed throughout the whole core, and Co and Mn were found atgreater concentrations in the coating layer on a surface of the corecompared to those in the core.

Therefore, it was confirmed that only the surface of the core was coatedwith LiMnCoO₄ and had a coating layer.

As shown in FIGS. 6B to 6E, it was confirmed that Co and Mn were foundat relatively high concentrations in the grain boundary between primaryparticles in the core and in the coating layer on a surface of the core.

As shown in FIG. 6C, it was confirmed that Mn was found at relativelyhigh concentrations in the grain boundary between primary particles inthe core and on a surface of the core but at a very low concentration inthe primary particles.

As shown in FIG. 6E, it was confirmed that Ni and Mn were found at thesame time, and Ni was disposed in the primary particles whereas Mn washardly found in the primary particles but found at a high concentrationin the grain boundary between the primary particles and on a surface ofthe core.

In FIG. 6B, location of Co was not significant, but referring to FIG. 6Dwhere Ni and Co are both shown, Co shown in green was found in the grainboundary including Ni between the primary particles and on a surface ofthe core.

In FIG. 6F, Ni, Co, and Mn are shown at the same time. It was confirmedthat Ni was found in the primary particles in the core, Co and Ni werefound between the primary particles, and Co and Ni were found on asurface of the core. In FIG. 6F, Mn in red and Co in green areoverlapped and thus shown in orange.

Therefore, it was confirmed that LiMnCoO₄ was evenly coated on all ofthe core surface and in the grain boundary between the primary particlesin the core.

Evaluation Example 4: Evaluation of Amount of Lithium Residue

Amounts of lithium residue on surfaces of the composite cathode activematerials prepared in Examples 1 to 4 and Comparative Examples 1 and 2were measured, and some of the results are shown in Table 1.

The amounts of the lithium residue were evaluated by measuring Liamounts in LiCO₃ and LiOH remaining on a surface of the compositecathode active material by using a wet method (or a titration method).

Details about the measuring method may be, for example, found inparagraph [0054] of Japanese Patent No. 2016-081903, the content ofwhich is incorporated herein, in its entirety, by reference.

TABLE 1 Amount of lithium residue (ppm) Comparative Example 1 2552Comparative Example 2 2127 Example 1 1626 Example 2 1429 Example 3 1174

As shown in Table 1, amounts of lithium residues of the compositecathode active materials of Examples 1 to 3 decreased compared to thatof the composite cathode active material of Comparative Example 1.

While not wanting to be bound by theory, it is believed that suchdecrease may have been a result of the fact that a coating layer havinga spinel structure formed on a surface of and inside the core as aresult of a reaction between the lithium residue on a surface of thefirst lithium transition metal oxide and a precursor of the secondlithium transition metal oxide.

Therefore, gas occurrence during a charge/discharge of a lithium batteryincluding each of the composite cathode active materials prepared inExamples 1 to 3 may be suppressed, and thus deterioration of lifetimecharacteristics may be suppressed.

Evaluation Example 5: Charge/Discharge Characteristic Evaluation

At a temperature of 25° C., each of the lithium batteries prepared inExamples 5 to 8 and Comparative Examples 3 and 4 was charged at aconstant current of 0.1 C rate until a voltage was 4.35 V (vs. Li), andthen while maintaining the voltage at 4.35 V in a constant voltage mode,the current was cut-off at a current of 0.05 C rate. Next, the batterieswere each discharged at a constant current of 0.1 C rate until a voltagewas 2.8 V (vs. Li) (the 1^(St) cycle, a formation process).

At 25° C., each of the lithium batteries that underwent the 1^(st) cyclewas charged at a constant current of 0.33 C rate until a voltage was4.35 V (vs. Li), and then while maintaining the voltage at 4.35 V in aconstant voltage mode, the current was cut-off at a current of 0.05 Crate. Next, the batteries were each discharged at a constant current of0.2 C rate until a voltage was 2.8 V (vs. Li) (the 2^(nd) cycle).

At 25° C., each of the lithium batteries that underwent the 2^(nd) cyclewas charged at a constant current of 0.33 C rate until a voltage was4.35 V (vs. Li), and then while maintaining the voltage at 4.35 V in aconstant voltage mode, the current was cut-off at a current of 0.05 Crate. Next, the batteries were each discharged at a constant current of0.3 C rate until a voltage was 2.8 V (vs. Li) (the 3^(rd) cycle).

At 25° C., each of the lithium batteries that underwent the 3^(rd) cyclewas charged at a constant current of 0.33 C rate until a voltage was4.35 V (vs. Li), and then while maintaining the voltage at 4.35 V in aconstant voltage mode, the current was cut-off at a current of 0.05 Crate. Next, the batteries were each discharged at a constant current of1 C rate until a voltage was 2.8 V (vs. Li) (the 4^(th) cycle).

At 25° C., each of the lithium batteries that underwent the 4^(th) cyclewas charged at a constant current of 0.33 C rate until a voltage was4.35 V (vs. Li), and then while maintaining the voltage at 4.35 V in aconstant voltage mode, the current was cut-off at a current of 0.05 Crate. Next, the batteries were each discharged at a constant current of2 C rate until a voltage was 2.8 V (vs. Li) (the 5^(th) cycle).

At 25° C., each of the lithium batteries that underwent the 5^(th) cyclewas charged at a constant current of 0.33 C rate until a voltage was4.35 V (vs. Li), and then while maintaining the voltage at 4.35 V in aconstant voltage mode, the current was cut-off at a current of 0.05 Crate. Next, the batteries were each discharged at a constant current of3 C rate until a voltage was 2.8 V (vs. Li) (the 6^(th) cycle).

At 25° C., each of the lithium batteries that underwent the 6^(th) cyclewas charged at a constant current of 0.33 C rate until a voltage was4.35 V (vs. Li), and then while maintaining the voltage at 4.35 V in aconstant voltage mode, the current was cut-off at a current of 0.05 Crate. Next, the batteries were each discharged at a constant current of1 C rate until a voltage was 2.8 V (vs. Li) (the 7^(th) cycle), and thiscycle was repeated 50 times under the same conditions until the 56^(th)cycles.

10 minutes of retention time was allowed after each set ofcharge/discharge cycles in the whole charge/discharge cycles.

Some of the results of the charge/discharge test are shown in Table 6. Acrack growth at the 56^(th) cycle, a capacity retention at the 56^(th)cycle, and an initial charge/discharge efficiency and high ratecharacteristic at the 1^(st) cycle are defined by Equations 2 to 5, eachrespectively.

$\begin{array}{l}{\text{Crack growth}(\%) = \lbrack ( \text{pore area of cross-section of composite} ) )} \\{\text{cathode active material particles after the 56}^{\text{th}}\text{cycle - pore area of}} \\\text{cross-section of composite cathode active material particles after the} \\{\text{6}^{\text{th}}\text{cycle / pore area of cross-section of composite cathode active}} \\{( {\text{material particles before the 6}^{\text{th}}\text{cycle}} \rbrack \times 100\%}\end{array}$

$\begin{array}{l}{\text{Capacity retention}(\%) = \lbrack {\text{Discharge capacity at the 56}^{\text{th}}\text{cycle /}} )} \\{( {\text{Discharge capacity at the 7}^{\text{th}}\text{cycle}} \rbrack \times 100\%}\end{array}$

$\begin{array}{l}{\text{Initial efficiency}(\%) = \lbrack {\text{Discharge capacity at the 1}^{\text{st}}\text{cycle /}} )} \\{( {\text{Charge capacity at the 1}^{\text{st}}\text{cycle}} \rbrack \times 100\%}\end{array}$

$\begin{array}{l}{\text{High rate characteristic}(\%) = \lbrack {\text{Discharge capacity at the 4}^{\text{th}}\text{cycle}} )} \\{( {( {2\text{C rate}} )\text{/Discharge capacity at the 2}^{\text{nd}}\text{cycle}( {0.2\text{C rate}} )} \rbrack \times 100\%}\end{array}$

TABLE 2 Charge capacity at the 1^(st) cycle (mAh/g) Initial efficiency(%) High rate characteristic (%) Discharge capacity at the 7^(th) cycle(mAh/g) Capacity retention (%) Crack growth (%) Comparative Example 3247 92 88 190 69.6 6.5 Comparative Example 4 239 90 92 200 90.9 -Example 5 229 90 92 200 90.9 - Example 6 243 88 94 205 92.6 - Example 7246 91 92 210 93.3 5.7

As shown in Table 2, the lithium batteries of Examples 5 to 7 hadsignificantly improved capacity retentions compared to that of thelithium battery of Comparative Example 3 including an uncoated compositecathode active material.

In the lithium batteries of Examples 5 to 7, the composite cathodeactive material further includes a shell in the form of a coating layerhaving a spinel crystal structure, which has 3-dimensional lithium iontransferring pathways, on a layered core. Thus, while not wanting to bebound by theory, it is believed that that capacity retentions of thelithium batteries of Examples 5 to 7 significantly improved because thecomposite cathode active material added with a coating layer having aspinel crystal structure on a surface thereof has improvedcharge/discharge characteristics provided by the lithium iontransferring pathways, compared to the composite cathode active materialof Comparative Example 1 which only has a layered crystal structure.

Also, discharge capacities and capacity retentions of the lithiumbatteries of Examples 5 to 7 were the same or improved compared to thoseof the lithium battery of Comparative Example 4 including the compositecathode active material only coated on a surface of the core.Particularly, both a discharge capacity and a capacity retention of thelithium battery of Example 6 including the composite cathode activematerial coated with a spinel layer at the same amount with that of thelithium battery of Comparative Example 4 improved.

While not wanting to be bound by theory, it is believed that suchimprovement may have been a result of the fact that the compositecathode active material in the lithium batteries of Examples 5 to 7further includes a coating layer having a spinel crystal structure thatprovides 3- dimensional lithium ion transfer pathways in a grainboundary between primary particles in a layered core, which facilitateslithium ion conduction in the core, and thus elution of metal ions fromthe primary particles in the layered core to an electrolyte solution issuppressed. Also, it is believed that a side reaction with theelectrolyte solution in the grain boundary between the primary particlesin the layered core is suppressed.

Further, in the lithium battery of Example 7, a crack growth of thecomposite cathode active material decreased and thus mechanical strengthof the composite cathode active material increased, compared to that ofthe lithium battery of Comparative Example 3. This decreased of thecrack growth is believed to have been a result of the fact that thecoating layer having a spinel crystal structure disposed in the grainboundary between the primary particles absorbed volume change of theprimary particles according to the charge/discharge process andsuppressed crack between the primary particles.

As described above, according to an aspect of one or more embodiments,when a composite cathode active material includes a composition having aspinel crystal structure in a core and on a surface of the core,charge/discharge characteristics of a lithium battery including thecomposite cathode active material may improve.

It should be understood that embodiments described herein shall beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould be considered as available for other similar features or aspectsin other embodiments.

While an embodiment has been described with reference to the figures, itwill be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope as defined by the following claims.

What is claimed is:
 1. A composite cathode active material comprising: acore comprising a plurality of primary particles comprising anickel-containing first lithium transition metal oxide having a layeredcrystal structure, and a grain boundary between adjacent primaryparticles of the plurality of primary particles; and a shell on thecore, the shell comprising a second lithium transition metal oxidehaving a spinel crystal structure, wherein the grain boundary comprisesa first composition having a spinel crystal structure, wherein aconcentration of cobalt in the grain boundary is greater than aconcentration of cobalt in the primary particles, and wherein the secondlithium transition metal oxide is represented by Formula 7:

wherein, in Formula 7, M5′ comprises vanadium, chromium, iron,zirconium, rhenium, aluminum, boron, germanium, ruthenium, tin,titanium, niobium, molybdenum, or platinum, $\begin{array}{l}{0.9 \leq \text{a} \leq 1.1,\mspace{6mu}\, 0 \leq \text{b} < \text{2}\text{.0,}\,\text{0} < \text{c} < \text{2}\text{.0,}\,\text{0} \leq \text{d} < \text{0}\text{.1,}} \\\text{and b + c + d=2}\end{array}$ .
 2. The composite cathode active material of claim 1,wherein the first composition comprises at least one transition metalother than nickel, and wherein a concentration of the at least onetransition metal other than nickel in the grain boundary is greater thana concentration of the at least one transition metal other than nickelwithin the plurality of primary particles.
 3. The composite cathodeactive material of claim 2, wherein the least one transition metal otherthan nickel comprises Mn, Fe, or a combination thereof.
 4. The compositecathode active material of claim 1, wherein at least 50% of the grainboundaries between the adjacent primary particles of the plurality ofprimary particles comprise the first composition.
 5. The compositecathode active material of claim 1, wherein the grain boundary issubstantially rectilinear in cross-section within the core.
 6. Thecomposite cathode active material of claim 1, wherein the grain boundaryis arranged in a direction which is parallel to a surface of an adjacentprimary particle of the adjacent primary particles, and wherein thedirection of the grain boundary is different from a direction of atangent of a nearest surface of the core.
 7. The composite cathodeactive material of claim 1, wherein the core comprises a first grainboundary and a second grain boundary, wherein the first grain boundaryand the second grain boundary are located directly on a same primaryparticle of the plurality of primary particles, and wherein the firstgrain boundary and the second grain boundary intersect at an angledetermined by a shape of the same primary particle.
 8. The compositecathode active material of claim 1, wherein the core comprises aplurality of grain boundaries that are adjacent to the plurality ofprimary particles, wherein the plurality of grain boundaries are eacharranged in a direction parallel to a surface of an adjacent primaryparticle, and wherein grain boundaries of the plurality of grainboundaries are arranged in different directions than each other.
 9. Thecomposite cathode active material of claim 1, wherein a plurality ofgrain boundaries have an average length in a range of about 50nanometers to about 1000 nanometers and an average thickness in a rangeof about 1 nanometers to about 200 nanometers, wherein a direction ofthe length is parallel to a surface of an adjacent primary particle, andwherein a direction of the thickness is perpendicular to the surface ofthe adjacent primary particle.
 10. The composite cathode active materialof claim 1, wherein the spinel crystal structure has cubic symmetry andbelongs to an Fd3m space group.
 11. The composite cathode activematerial of claim 1, wherein the grain boundary further comprises asecond composition, and wherein the second composition comprises alithium transition metal oxide, a lithium-free transition metal oxide,or a combination thereof.
 12. The composite cathode active material ofclaim 11, wherein the second composition has an amorphous structure, alayered structure, a spinel structure, a polyvalent anion crystalstructure, or a combination thereof.
 13. The composite cathode activematerial of claim 1, wherein the nickel-containing first lithiumtransition metal oxide is represented by Formula 1:

wherein, in Formula 1, M comprises nickel and at least one non-nickelGroup 4 to Group 13 element, an amount of nickel is in a range of about70 mole percent to less than about 100 mol percent, based on a totalcontent of M, and 0.9≤a≤1.1.
 14. The composite cathode active materialof claim 1, wherein the nickel-containing first lithium transition metaloxide is represented by Formula 2:

wherein, in Formula 2, M1, M2, and M3 are different and eachindependently comprises manganese, vanadium, chromium, iron, cobalt,zirconium, rhenium, aluminum, boron, germanium, ruthenium, tin,titanium, niobium, molybdenum, or platinum; and $\begin{array}{l}{0.9 \leq \text{a} \leq \text{1}\text{.1,  0}\text{.7} < \text{b} < \text{1}\text{.0,  0} < \text{c} < \text{0}\text{.3,  0} < \text{d} < \text{0}\text{.3,}} \\{\text{0} \leq \text{e} < \text{0}\text{.1, and b+c+d+e = 1}}\end{array}$ .
 15. The composite cathode active material of claim 1,wherein the nickel-containing first lithium transition metal oxide isrepresented by Formula 4c:

wherein, in Formula 4c, M″ comprises nickel and cobalt, manganese,vanadium, chromium, iron, zirconium, rhenium, aluminum, boron,germanium, ruthenium, tin, titanium, niobium, molybdenum, platinum, or acombination thereof, and 0 < a < 1 .
 16. The composite cathode activematerial of claim 1, wherein a thickness of the shell is about 300nanometers or less.
 17. The composite cathode active material of claim1, wherein a sum of an amount of the second lithium transition metaloxide and an amount of the first composition is about 10 weight percentor less, based on a total weight of the composite cathode activematerial.
 18. The composite cathode active material of claim 1, whereina crack growth of a cross-section of the composite cathode activematerial after 50 charge/discharge cycles of a lithium batterycomprising the composite cathode active material is about 6% or less,and wherein the crack growth is defined by Equation 1: $\begin{array}{l}{\text{Crack growth}(\%) = \lbrack ( \text{pore area of cross-section of composite} ) )} \\\text{cathode active material particles after 50 charge/discharge cycles - pore} \\\text{area of cross-section of composite cathode active material particles before} \\{\text{charge/discharge}( \text{cycles} )/\text{pore area of cross-section of composite cathode}} \\{\text{active material particles before charge/discharge}( \text{cycles} \rbrack \times 100}\end{array}$ .
 19. A cathode comprising the composite cathode activematerial of claim
 1. 20. A lithium battery comprising: the cathode ofclaim 19; an anode; and an electrolyte between the cathode and theanode.